A coherent optical communication system occupies an important position in a communication transmission network for its huge transmission bandwidth, great potential for expansion, extremely low transmission loss and low cost. It is key to select an appropriate modulation format in building a coherent optical communication network of low cost, large capacity and high spectral efficiency. In recent years, flexible and variable modulation formats have become hot spots as the most effective way to increase transmission rates. High-order quadrature amplitude modulation (QAM) is becoming a mainstream solution for next-generation optical communication systems. And a complex QAM modulation format is particularly sensitive to phase noises.
Existing phase noise compensation methods are generally based on a blind phase search scheme or a carrier phase estimation scheme based on interleaving quadrature phase shift keying (QPSK) to compensate for phase noises caused by a laser.
It should be noted that the above description of the background is merely provided for clear and complete explanation of this disclosure and for easy understanding by those skilled in the art. And it should not be understood that the above technical solution is known to those skilled in the art as it is described in the background of this disclosure.